Download (Angiosperm Gen . Ch.(Anurita))

Dr. Anurita Sharma
Assistant Professor
Department of Botany
Post Graduate Govt. College For Girls
Sector-11, Chandigarh
 Angiosperm means "contained seeds“ , the
ovules are sealed within the carpel and the
seeds sealed within a fruit.
 The flowering plants or angiosperms
emerged in the Cretaceous period, some 130
million years ago. These sporophytes
dominate the landscape around us and are
the most successful plant group, with
something like a quarter of a million species
described.
 Plant body is divided into true roots, stem and
leaves.
 Sporophytic generation is the dominant phase
represented by the plant body.
 Gametophytic generation is reduced and is
totally dependent on sporophyte.
 Flowers display plant’s male and female parts
and are sites of pollination and fertilization.
 Generate fruits, which contain seeds.
• Most of the Angiosperms are
autotrophic and have a green pigment
chlorophyll for photosynthesis.
• A few species lack chlorophyll and
become parasitic, e.g., Cuscuta ,
Viscum.
• Some plants are insectivorous, e.g.,
Nepenthes, Drosera.
Cuscuta common name Dodder is a
stem holoparasite.
INSECTIVOROUS PLANTS
Drosera (Sundew)
Nepenthes ( Pitcher plant)
• Based on habitat Angiosperms are mainly of three
types:
1.Hydrophytes:
These plants grow in aquatic habitats. They have
developed aerenchyma and a covering of mucilage.
They may be submerged or floating .
2.Mesophytes:
These are terrestrial plants growing under
moderate moisture temperate conditions.
3.Xerophytes:
These are terrestrial plants of dry habitat. They
develop adaptations to reduce transpiration and to
retain water.
HYDROPHYTES
Lemna
Hydrilla
Nymphaea
Mesophytes
Sunflower
Petunia
XEROPHYTES
Opuntia
Nerium
Duration and Habit
Duration - the life span of an individual plant.
Annual - plants live for a single growing season;
Biennial - lives for two seasons;
Perennial - lives for three or more years and
usually flowers and fruits repeatedly.
Habit - the general appearance of a plant.
Tree - plant with woody tissue present in one
primary trunk;
Shrub - plant with woody tissue present in several
trunks and usually shorter than trees;
Herb - plant lacking woody tissue;
Liana - climbing plant with woody stems;
Vine - climbing plants with herbaceous (nonwoody) stems.
Angiosperms (Flowering Plants)
Systematists have identified angiosperms into two subgroups: Monocotyledonous and dicotyledonous.
Monocots are angiosperms that possess one embryonic
seed leaf (cotyledon).
Dicots are angiosperms that possess two embryonic seed
leaves (cotyledons).
Feature
Monocot
Dicot
two
one cotyledon
cotyledons
Seedling
branching
Leaf venation often parallel
or net-like
Flower parts
Secondary
growth
Roots
often 4, 5 or
often in threes
many
never truly
woody
tap root fibrous
can be
woody or
herbaceous
A COMPARISON OF MONOCOTS & DICOTS
The vegetative parts of angiosperms are
roots, stems, and leaves, and the
reproductive parts are flowers, fruits, and
seeds. Here we outline parts, particularly
as they refer to angiosperms.
Roots
Adventitious - developing from any plant part other than the
embryonic root or another root.
Fibrous - with all portions of the root system being of more or
less equal thickness, often well branched.
Taproot - the major root, usually enlarged and growing
downward.
Stems
Stem —the axis of plants—consists of nodes (where
leaves and axillary buds are produced)
separated by internodes.
Node - region of the stem where the leaf and bud are borne.
Internode - the part of the stem between two adjacent nodes.
Herbaceous - not woody; dying down at the end of the growing
season.
Woody - hard in texture, containing secondary xylem, and
persisting more than one growing season.
Acaulescent - having an inconspicuous stem.
Caulescent - having a distinct stem.
Bulb - a short, erect, underground stem surrounded by thick,
fleshy leaves or leaf bases.
Corm - a short, erect, underground, more or less fleshy stem
covered with thin, dry leaves or leaf bases.
Rhizome - a horizontal stem, more or less underground, bearing
scale-like leaves; often called a stolon if above ground and having
an elongated internode.
Scape - an erect leafless stem bearing an inflorescence or flower.
Thorn - a reduced, sharp-pointed stem.
Tuber - a swollen, fleshy portion of a rhizome involved in water or
carbohydrate storage.
Buds
Buds are short embryonic stems. In angiosperms they are
found at the nodes, in the leaf axil (the angle formed by the
stem and the petiole of the leaf).
Axillary bud - a bud located in the leaf axil.
Terminal bud - a bud at the apex of a stem.
Leaves
Leaves are the major photosynthetic parts of most plants. They
are borne at the nodes of a stem, usually below a bud. They
are usually flat, and have one surface facing towards the stem
axis (the adaxial, or upper, surface) and another surface facing
away from the stem axis (the abaxial, or lower, surface).
Leaves are homologous structures among the angiosperms,
but not among vascular plants as a whole. In addition to the
obvious function in photosynthesis, leaves may be modified for
protection, forming sharp pointed spines; for water storage, as
in many succulents; for climbing, as in vines and lianas with
tendril leaves; for capturing insects, as in carnivorous plants; or
providing homes for ants or mites.
The major parts of the leaf are shown below. In monocots
the leaf is almost always broadly sheathing at the base. In
taxa such as grasses and gingers there is an adaxial flap or
ligule at the junction of the sheath and blade.A leaf
thatlacks a petiole is said to be sessile.
Pulvini (singular pulvinus) - somewhat swollen
and morphologically distinct parts of the
petiole, are often
present and involved in
leaf movement.
Stipules - usually paired appendages located
on either side of (or on) the petiole base.
Leaf Arrangement - Leaves may be arranged in one of three
major patterns:
Alternate leaves are arranged singly and are usually arranged
in a spiral pattern along the stem. Alternate leaves are
sometimes placed along just two sides of the stem (2-ranked, or
distichous), or only three sides of the stem (3-ranked, or
tristichous).
Opposite leaves are borne in pairs, the members of which are
positioned on opposite sides of the stem. A common pattern for
opposite leaves is for each successive set of paired leaves to
be rotated 90 degrees (decussate).
When three or more leaves are positioned at a node, they are
considered to be whorled.
Leaf Structure - A leaf with a single blade is
termed simple; a leaf with two or more blades,
or leaflets, is said to be compound. The
distinction between simple and compound
leaves can be made by locating the axillary bud:
an axillary bud is subtended by an entire leaf
and never by individual leaflets. Leaflets can be
arranged in various ways, including evenpinnate, odd-pinnate, palmate, trifoliate, and
twice-pinnate.
Leaf Duration - Leaves may function from a few days to many
years, but most leaves function for only one or two growing
seasons. Deciduous leaves fall at the end of the growing
season; evergreen plants are leafy throughout the year.
Venation Types - If there is one most prominent vein in a leaf,
it is called the midvein or primary vein; branches from this vein
are called secondary veins. Tertiary veins usually link the
secondaries, forming a ladderlike or netlike (reticulate)
pattern.
There are three major patterns of organization of
the major veins. The leaf may have a single
primary vein with the secondary veins arising
along its length like the teeth of a comb; this
pattern is termed pinnate. Or the leaf may have
several major veins radiating from the base of the
blade; this pattern is called palmate. Finally, the
leaf may have many parallel veins, a pattern
termed parallel venation.
• An important characteristic of Angiosperms is a
flower. It is a modified condensed shoot meant
essentially for the reproduction of the plant.
• The flower arises in the axil of a leaf supported
by a stalk called as pedicel.
• The upper swollen end of the pedicel called as
receptacle or torus or thalamus bears all the floral
parts.
• A flower consists of four whorls of floral leaves –
calyx, corolla, androecium and gynoecium.
• Calyx and corolla are sterile, non-essential
accessory whorls.
• Androecium and gynoecium are fertile, essential
reproductive whorls.
Flower -sepals, petals, stamens, carpels.
Sepal (calyx) -before flower opens,
sepals enclose and protect flower bud.
Petal (corolla) -advertises flower to
insects and other pollinators.
Flower’s reproductive organs: stamen
and carpel.
Stamen (androecium) -male organ.
Carpel (gynoecium) -female organ.
Ovary -base of the carpel. Houses ovules.
Ovule -contains developing egg and cells
that support it.
PARTS OF A FLOWER
 In the simplest flowers the parts are arranged
successively - calyx, corolla, androecium,
gynoecium (hypogynous flower, superior
ovary). In some flowers (Rosaceae) the
receptacle grows up around the ovary into a
kind of cup (perigynous flower, superior
ovary) and in others the other parts are joined
to the top of the ovary (epigynous flower,
inferior ovary).
DOUBLE FERTILIZATION
Refers to a process in which two sperm cells
fertilize cells in the ovary. This process begins when
a pollen grain adheres to the stigma of the pistil
(female reproductive structure), germinates, and
grows a long pollen tube. While this pollen tube is
growing, a haploid generative cell travels down the
tube behind the tube nucleus. The generative cell
divides by mitosis to produce two haploid (n) sperm
cells.
The pollen tube enters into the ovule, through the
micropyle. Inside the embryo sac, the tip of the
pollen tube ruptures and the 2 male gametes are
set free near the egg apparatus. Inside the embryo
sac, one of the 2 male gametes fuses with the egg
nucleus and forms a diploid zygote. This process
is called syngamy or true fertilisation. The other
male gamete pushes further into the embryo sac
and fuses with the secondary nucleus and gives
rise to a triploid nucleus called the primary
endosperm nucleus. This process of nuclear
fusion is called triple fusion.
DOUBLE FERTILIZATION
This entire phenomenon of fertilisation involving
the fusion of the egg and one of the male
gametes, together with the union of the second
male gamete with the secondary nucleus or the
polar nuclei is called as double fertilisation.
DOUBLE FERTILIZATION
As the zygote develops into an embryo, the
triploid cell develops into the endosperm, which
serves as the embryo's food supply. The ovary
now will develop into fruit and the ovule will
develop into seed.
LIFE CYCLE OF AN ANGIOSPERM
Features that enhanced success
of angiosperms
• Evolution of mutually dependent relationships
with animals (carry pollen more reliably then
wind).
• Ability to reproduce rapidly (fertilization occurs
12 hours after pollination, making it possible for
plant to produce seeds in few days or weeks).
INTERACTIONS WITH ANIMALS-PROFOUNDLY
INFLUENCED ANGIOSPERM EVOLUTION
• Flowering plants and land animals have mutually
beneficial relationships throughout their evolutionary
history.
• Most angiosperms depend on birds, insects and
mammals for pollination and seed dispersal.
• Most land animals depend on angiosperms for food.
• Mutual dependency improves reproductive success
of both and thus is favoured by natural selection.
Bees are attracted to flowers that have markings that
reflect UV light. As bee feeds on nectar, it picks up
pollen.
Flowers that attract hummingbirds have nectar located deep
in floral tube where only the long, thin beak and tongue of
that bird can reach.Picks
up pollen on beak and feather while feeding.
Some flowering plants depend on nocturnal pollinators such as
bats.
These plants have large, light-coloured highly scented flowers that
can be easily found at night. Anther dusts bat’s hair with pollen
and passes onto other flowers.